A recombinant Lyme vaccine based on a preparation of outer surface protein A (OspA) is now approved for human use in the U.S. Since the most widely used serologic tests for Lyme disease utilize a whole-cell sonicate of OspA-containing B. burgdorferi, false positives from vaccinated persons are common. To avoid false positives from vaccinated subjects, they will develop and evaluate novel immunoassays incorporating variants of B. burgdorferi which lack the OspA encoding plasmid. Preliminary data suggest that an Osp-A-negative ELISA test is useful for discriminating the vaccinated state from vaccine failure in humans; sera from subjects participating in a vaccine trial yielded false positive results with an OspA-containing ELISA, but no such reactivity was observed with the OspA-negative ELISA. Moreover, in cases of vaccine failure, the new ELISA and western blot tests are capable of identifying such cases under circumstances in which tests performed with conventional antigens are difficult or impossible to interpret. To refine testing for Lyme disease, five naturally-occurring genetic variants will be evaluated in novel antibody capture ELISA and Western blot formats to determine which strain or strain combination provides the greatest sensitivity and specificity in a panel of clinically well-characterized sera (400 Lyme patients and 400 control patients). These new tests will offer enhanced sensitivity, specificity, and will correctly identify B. burgdorferi infection in vaccinated and non-vaccinated patients. PROPOSED COMMERCIAL APPLICATION: Proposed commercial application is to develop assays utilizing OspA negative reagents for use in commercial diagnostic settings for the diagnosis of Lyme infection in vaccinated or non-vaccinated subjects.